The invention relates to lock systems, particularly heavy duty lock systems, useful for example in exit and entry control hardware for commercial and public structures.
Heavy duty door latching and locking hardware, because of its typically rugged construction and of the stresses to which it is subjected, is susceptible to binding particularly in the latchbolt which in most prior art designs is adapted to be slid in and out of its keeper in rectilinear or sliding movements. For example, the pressure of people against a door when attempting an emergency exit can so stress a dead latched latchbolt that severe binding can occur. Panic bars are typically designed to overcome such stresses by brute force, although the strains on the internal linkage can approach the breaking point.
In normal non-emergency use the relatively small torque generated by a hand key is often inadequate to withdraw a latchbolt in which binding has occurred as a result for example of a poor fit in the keeper.
The present invention has for its object to overcome these and other disadvantages of prior art designs by providing a dual direction swinging mount for the latchbolt which enables it to swing in one direction to release the door for opening and to swing in the other direction to permit re-latching when the door closes. Dual dead latches are also provided to secure the latchbolt from unauthorized release in either direction of swinging movement. The latchbolt is contoured to present camming surfaces to the keeper for both directions of door movement and is further contoured on an inner edge to clear the primary dead latch linkage after initial release occurs.
The primary dead latch opposes swinging movement of the latchbolt out of its keeper under the pressure of the camming surface of the latchbolt engaging the keeper when an attempt is made to open the door. When released from its dead latch the latchbolt is cammed out of its keeper by the movement of the opening door. Thus the latchbolt becomes a passive rather than active element in the door unlocking process. The primary dead latch includes a double-armed rock shaft carrying a roller between its arms which blocks the swinging movement. The dead latch assembly is normally backed against stops by a spring causing it to assume a position in which it is over-centered or toggled so that the force on the latchbolt serves only to seat the dead latch more firmly. Release of the primary dead latch can be effected for example through a key-operated linkage in which the key through linkage swings the double arm rocker through a sufficient angle to pass over the center point of the toggle at which time movement of the door causes the keeper to operate on the front cam surface of the latchbolt to swing the latchbolt out of its latching position. Once out of the keeper, the spring of the rocker arms pushes the latchbolt back to its outermost position. It will be understood that the primary dead latch can also be released by other mechanisms, such for example as a panic bar, which when moved causes the rocker arms to swing through a sufficient angle to clear the latchbolt from its dead latch position.
The secondary dead latch, which prevents swinging of the latchbolt in the opposite direction, includes a tiltable latch plate, spring biased to a position which normally engages the end of the latchbolt remote from that of the primary dead latch. Thus the latchbolt cannot be "picked" by inserting a tool into the space between the keeper and the latchbolt housing.
When a door is opened pursuant to authorized release, once past the keeper the latchbolt swings back out to its normal position. Concurrently with this outward swinging movement, a feeler arm which is normally held in the edge of the keeper, swings outwardly under a spring biasing carrying with it a camming surface which moves the latch plate of the secondary dead latch away from and clear of the latchbolt thereby freeing the latchbolt to swing inwardly as the door closes. A rearwardly facing camming surface on the latchbolt engages the edge of the keeper to force the latchbolt inwardly allowing it to relatch. The feeler finger is also cammed inwardly at the same time but does not enter the keeper aperture but rather remains in its inward position thereby permitting the dead latch plate to assume the latching position in the path of swinging movement of the latchbolt.